1. Field of the Invention
This invention relates to photographic camera apparatus, and, more particularly, to the structural configuration of a thin, normally flat, flexible shutter which may be bowed to follow the lens of a simple type camera in a predetermined manner as the lens is adjusted for focus.
2. Description of the Prior Art
Simple lenses having fixed focal lengths, such as the classical single element meniscus landscape lens, have often been used in box or rigid body type cameras because they are inexpensive, easy to manufacture, and are perfectly satisfactory for many photographic applications, particularly those of the amateur photographer. However, in order to obtain sharply imaged photographs with cameras utilizing these simple lenses, it is generally necessary to provide some means for changing the actual distance between the lens and the film in accordance with the distance separating the lens from the object it is to image. Adjusting the lens to film distance is, of course, known as focusing, and the amount of focusing required is related to the focal length of the particular lens being used and the object distance.
There are several well known ways of changing the focus distance. For example, one popular way is to provide a helical focusing mount in which the lens can be rotated to screw it towards or away from the film. Another involves the use of a rack and pinion arrangement where the rack is attached along the length of a cylindrical tube in which the lens is mounted and the pinion is mounted with the camera housing and engaged with the rack. The photographer, in this case, simply rotates the pinion through some suitable means to move the cylindrical mount and lens as a unit toward or away from the film.
Another way of focusing is disclosed in U.S. Pat. No. 3,902,792 issued to William T. Plummer on Sept. 2, 1975 and entitled "Landscape Lens" where the patentee describes an improved landscape lens which is mounted in a cylindrical sleeve which may be slid in a camera housing between two detent positions that are separated from the film plane by different amounts corresponding to a short back focal length for objects which are far and a longer back focal length for nearer objects.
The foregoing focusing arrangements are quite effective when used in combination with the simple type lens and are attractive from an economic standpoint because of their simplicity. However, there are problems associated with these focusing arrangements when used with simple lenses of the fixed focus type.
One of those problems is related to the fact that aperture stops often play an important role in the quality of the image formed by a simple lens. As an example consider the familiar landscape lens again. This consists of a simple positive meniscus lens element and an aperture stop. In this lens the aperture stop is used to minimize the coma aberration. Moreover, it is also well known that there is an optimum location on the concave side of a meniscus lens element for the purpose of reducing coma and that the allowable tolerance by which the aperture stop may deviate from the optimum location is very small especially compared with the distance by which such a lens would have to travel with respect to the film for proper focus over some reasonable range of object distances, say, 3.0 meters to .infin.. All this means is that the spatial relationship between the aperture stop and the meniscus lens element must be maintained substantially constant as such a lens is focused. Normally this presents no problem since the meniscus lens element and the aperture stop can be moved as a unit. However, when a shutter is introduced, the situation becomes more complicated because the aperture associated with the shutter may interfere with the coma correcting stop's function or actually take over its function if proper precautions are not exercised.
There are two known ways of solving this problem. The first is to provide a stationary shutter whose aperture is sufficiently large so that it never becomes part of the optical system or interferes with the coma correcting stop. In this manner, the lens may be focused with no degradation in image quality, but the shutter must, in general, be relatively large and probably relatively expensive as, for example, a focal plane type.
The second solution involves moving the entire shutter assembly with the lens to maintain some fixed shutter-to-lens distance as the lens is focused. This is a well known approach used in folding type cameras with accordian type bellows having erecting systems as those shown, for example, in U.S. Pat. No. 3,185,060 issued to R. S. Borghesani on May 25, 1965 and entitled "Photographic Apparatus" and U.S. Pat. No. 3,087,400 issued to E. R. Brandt on Apr. 30, 1963 and entitled "Folding Camera." It is also the approach suggested for use in a rigid body type camera such as that shown in FIG. 1 of previously referenced U.S. Pat. No. 3,902,792 issued to W. T. Plummer.
This second way, while satisfactory for folding type cameras having movable erecting systems, is not considered satisfactory for rigid body type cameras or folding cameras which erect into a fixed stationary configuration because it adds to camera size and requires that the entire shutter mechanism be moved in concert with the lens.
Consequently, there is a need for a simple compact shutter for tracking the focusing movement of a lens.
It is therefore a primary object of this invention to provide a simple compact shutter for tracking the focusing movement of a lens by flexing the shutter blade elements.
Other objects of this invention will in part be obvious and will in part appear hereinafter. The invention accordingly comprises the apparatus possessing the construction, combination of elements and arrangement of parts which are exemplified in the following detailed description.